Known enzymes active on nucleosides include those effecting hydrolysis or deamination thereof, and enzymes (nucleoside oxidases) for catalyzing the oxidation reaction thereof represented by the following equations. ##STR1##
Nucleoside oxidase is usually isolated from microorganisms typical of which is, for example, Pseudomonas putida, and the oxidase as purified is used for preparing nucleoside-5'-carboxylic acids, quantitative determination of nucleosides and systems for determining the activity of enzymes or the like wherein a nucleoside is produced or the amount thereof descreases due to a reaction.
However, in the oxidation reaction system wherein the oxidase is used, H.sub.2 O.sub.2 is inevitably produced, so that in producing the nucleoside-5'-carboxylic acid, the resulting H.sub.2 O.sub.2 needs to be decomposed by adding catalase to the reaction system. Further when the amount of H.sub.2 O.sub.2 produced in the reaction system is measured to quantitatively determine the nucleoside, the method has the disadvantage that peroxidase must be used. The method further has the disadvantage, for example, of necessitating a complex determination system (see, for example, Unexamined Japanese Patent Publications SHO 57-58883, SHO 57-68794 and SHO 57-94300).
We have conducted extensive research on nucleoside oxidases derived, for example, from microorganisms and found that a strain belonging to the genus Pseudomonas and newly isolated from soil has ability to produce an enzyme which catalyzes an oxidation reaction different from those involving the activity of the conventional nucleoside oxidases. We have also succeeded in isolating and purifying the enzyme, clarifying the characteristics thereof and developing novel assay or determination techniques utilizing the enzyme. Thus, the present invention has been accomplished.